The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. An intake valve is operated by drive of a camshaft, and air flows into the combustion chamber while the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Optimal operation of the intake valve/exhaust valve, however, depends on the RPM of the engine. That is, an appropriate time for lifting or opening/closing the valves depends on the RPM of the engine. In order to implement an appropriate valve operation in accordance with the RPM of the engine, as described above, a VVL (Variable Valve Lift) apparatus that operates valves at different lifts in accordance with the RPM of an engine has been studied.
Meanwhile, in a variable valve lift apparatus having a cam shift type which is configured that a plurality of cams are designed for driving a valve and the plurality of cams is moved along an axial direction, it is important that relative position between the plurality of cams and a valve opening/closing unit is exactly controlled.
In case that relative position between the plurality of cams and a valve opening/closing unit is not exactly controlled, interference is occurred between elements for guiding axial direction motion of the plurality of cams and the valve opening/closing unit or between the plurality of cams and the valve opening/closing unit. Thus, the valve opening/closing unit or the variable valve lift apparatus may be damaged, or reliability of a cam shift may be deteriorated.